Improve logging options

Issue our own log messages independently of the "debug" parameter, so a
user can activate our log messages through Python's standard logger
config features, while still having dsabled smtplib's debug messages,
which are very verbose and always go to stderr.

Change the log output for failed and ambiguous verifications from
"warning" to "info" as this is a normal function of the library and not
something that would require attention. Also this makes sure that no log
output is generated if logging is not configured at all (default is to
only display warning and above).

validate_email/mx_check.py

@@ -212,8 +212,7 @@ class _SMTPChecker(SMTP):
         return `True`, else raise exceptions described in `mx_check`.
         """
         for host in hosts:
-            if self.debuglevel > 0:
-                LOGGER.debug(msg=f'Trying {host} ...')
+            LOGGER.debug(msg=f'Trying {host} ...')
             if self._check_one(host=host):
                 return True
         # Raise appropriate exceptions when necessary

validate_email/validate_email.py

@@ -63,12 +63,8 @@ def validate_email(email_address: str, *args, **kwargs):
     try:
         return validate_email_or_fail(email_address, *args, **kwargs)
     except SMTPTemporaryError as error:
-        message = f'Validation for {email_address!r} ambigious: {error}'
-        if kwargs.get('debug'):
-            LOGGER.warning(msg=message)
+        LOGGER.info(msg=f'Validation for {email_address!r} ambigious: {error}')
         return
     except EmailValidationError as error:
-        message = f'Validation for {email_address!r} failed: {error}'
-        if kwargs.get('debug'):
-            LOGGER.warning(msg=message)
+        LOGGER.info(msg=f'Validation for {email_address!r} failed: {error}')
         return False